Objective: To determine whether there is a consistent extension of the lateral synovial recess under the iliotibial band (ITB) in an unembalmed cadaveric model. Design: A prospective laboratory investigation. Setting: A procedural skills laboratory of a tertiary medical center. Subjects: Twelve unembalmed cadaveric knee specimens. Methods: The suprapatellar recess, ITB, and region deep to the ITB were examined sonographically to document the absence of fluid in each knee. Thereafter, 60 mL of normal saline solution was injected into each knee to distend the joint recesses. Postinjection sonographic examination of the ITB at the level of the lateral femoral epicondyle was repeated at 0°, 25°, and 45° of knee flexion to detect and characterize any fluid visualized in the region of the ITB. The location of fluid in relation to the ITB was recorded as anterior, deep, posterior, or a combination of these positions. Results: Fluid was observed anterior and deep to the ITB in 100% of 12 specimens. In 2 specimens, fluid also was noted posterior to the ITB. The presence and location of the fluid did not appear to change as a function of knee position. Using dynamic sonographic evaluation, we could track the fluid deep to the ITB back to the knee joint. Conclusions: The lateral synovial recess appears to regularly extend beneath the anterior ITB. Fluid deep to the ITB should precipitate further evaluation of the knee joint when clinically indicated. Although distention of the lateral synovial recess is not always symptomatic, synovial irritation may be a pathoetiologic factor in the production of lateral knee pain syndromes, including ITB syndrome.